For what it’s worth here’s what Tandem Associates has to say about the subject.
https://www.tandem-associates.com/lionel/lionel_trains_2321_diesel.htm
And The Train Station shop in Mountain Lakes NJ.
OK- I just did some close examining of my 2321 under good lighting. Everyone is right, that the roof does look a little different in shade or color from the paintwork on the sides- but furthermore, the paint along the sides is not actually consistently the same looking shade. It looks lighter in all the outlines for the simulated doors and grills along the sides, and anywhere the paint might be thinner. Also, the roof appears glossier/smoother than the sides.
That said… I noted that the roof is not consistently the exact same shade either. It looks darker and less glossy towards the end of the long hood.
I believe the gloss/non gloss may simply be a matter of handling- the paint has been burnished slightly wherever hands tend to come into contact with the paint. That would explain why the maroon stripe, right behind the railing, doesn’t seem at all glossy. It is also a part of the loco I never took the time to dust, which may further add to the different appearence.
Another key thing to note- when I inspect places the gray paint has been chipped away on the body of the loco, I can see the maroon paint layer as well if I look carefully. It’s clearly more than one layer of paint. But where the maroon on the roof is chipped, it doesn’t appear like there is another layer of paint underneath.
I will add, the gray paint is so dirty that its shade also varies, depending how burnished it has become from handling. I really need to wash this poor thing somehow!! Eventually, eventually…
Anyhow, this is my conclusion: For whatever reason, the roof paint on my unit just didn’t stick. Who knows why. But it didn’t. And so the maroon is showing. And for whatever reason, this paint looks different in color depending how thick it is, and it wasn’t neccesarily applied perfectly evenly over the light gray plastic body.
Is it a “rare, collectable maroon top 2321”? No. It’s a gray-top unit with an unusual case of pai